Boxwood blight

Boxwood blight (also known as box blight or boxwood leaf drop) is a widespread fungal disease affecting boxwoods caused by Cylindrocladium buxicola (also called C. pseudonaviculatum).

History

The first description of boxwood blight was from the United Kingdom in the mid 1990s. In 2002 the disease was discovered in New Zealand, the cause was identified as a new species of fungus which was formally named Cylindrocladium pseudonaviculatum. The fungus causing the disease in the UK was later named C. buxicola. These are now known to be the same.^[1]

Boxwood blight is found throughout Europe,^[2]^[3] and has spread to North America. In October 2011 the blight was found in North Carolina and Connecticut. By January 2012 it had also been identified in Virginia, Maryland, Rhode Island, Massachusetts, Ohio, Oregon, Pennsylvania, New York and British Columbia.^[3] 2018 in Maine

Hosts

There appears to be some tolerance to the disease within the Buxus genus. In general, the boxwood varieties within the species sempervirens tend to be more susceptible to this disease; this would include the most popular varieties 'English' and 'American' boxwood.^[4] Other plants within the family Buxaceae, such as Pachysandra terminalis, as well as a Sarcococca species, have also found to be susceptible to this fungal pathogen.^{[citation needed]}

Symptoms and disease process

The blight initially presents as dark or light brown spots or lesions on leaves. The leaves typically turn brown or straw color, then fall off.^[5] The stems develop dark brown or black lesions.^[6] The disease is often fatal to young plants.

The spores remain viable for five years in fallen boxwood leaves,^[7] and are dispersed by wind and rain over short distances. Since they are sticky the spores may also be spread by birds, animals, and contaminated clothing and footwear. The most common mode of transmitting the blight is by the introduction of asymptomatic plants, or plants treated with fungicide (which can mask the disease) to unaffected areas.^[8] Warm and humid conditions facilitate its spread.^[9] The fungus does not need a wound to infect a plant, but it does require high humidity or free water.^[10]

Treatment

There is no known cure. Fungicides may prevent the spread of the disease. To be effective, they must be applied to the entire plant, leaves and stems, which can be difficult because boxwood leaves are very closely spaced.^[11]

Notes

^ Douglas. p. 1
^ Douglas pp. 1–2
^ ^a ^b Milius
^ http://go.ncsu.edu/boxwood_blight_links^{[permanent dead link]}^{[dead link]}
^ Douglas, p. 2
^ Milius quotes Lynn R. Batdorf, curator of the National Arboretum's boxwood collection (currently not infected): “I’ve never poured diesel fuel on a boxwood, but if I did, that’s what it would look like.”
^ Douglas, p. 7
^ Douglas, p. 6, calls this "Trojan horse " or "Typhoid Mary" transmission.
^ Douglas, p. 5
^ Douglas, p. 6
^ Douglas, p. 9 has details on various fungicides

References

Cylindrocladium buxicola: Taxonomy and References. Retrieved 26 December 2013.
Douglas, Sharon M. (December 2011). "Boxwood Blight - a new Disease for Connecticut and the U.S." (PDF). Connecticut Agricultural Experiment Station. Retrieved 26 May 2012.

Milius, Susan (20 January 2012). "Boxwood Blight Invades North America". Science News. Retrieved 26 May 2012.